This invention relates to aluminum dross and more particularly, it relates to the recovery of valuable products such as alumina and magnesia from a non-metallic product derived from the aluminum dross.
Aluminum dross results from the melting of aluminum scrap such as used beverage containers, aluminum siding, castings and the like and treating the melt with salt flux. The salt flux accumulates on top of the melt and forms a dross or skim which contains aluminum, oxides of aluminum and elements such as magnesium and silicon and other alloying elements present in the various alloys. Further, the skim contains other non-metallic products or compounds of the aluminum and alloying elements. The dross is removed or skimmed from the melt and processed usually to recover the metallic aluminum occluded in the oxides and non-metallic compounds. The aluminum can constitute 5 to 70% of the dross. Usually, the aluminum, which is considered the most valuable component, is recovered from the solidified dross by first fracturing the dross, for example, by mechanical milling and screening out the aluminum. Thereafter, fractured dross is heated in the presence of additional salt flux to free metallic aluminum. The molten salt flux aids in releasing molten aluminum from the dross. The salt flux is usually comprised of sodium chloride and potassium chloride. After a major portion of metallic aluminum is removed, the dross is comprised of three major components which are aluminum, salt flux and an insoluble constituent comprised largely of aluminum oxide, silicon oxide and magnesium oxide, and other non-metallic compounds. This processed dross is often referred to as salt cake. The three components can be present in the ranges of about 3 to 25 wt. % aluminum, 25 to 50 wt. % salt flux and 25 to 75 wt. % NMP. The NMP (non-metallic product) is comprised mainly of compounds such as oxides of aluminum, silicon and magnesium. Also, included in the salt cake are minor amounts of oxides and other compounds of titanium, copper, iron, calcium, zinc, sulfur, potassium and sodium which constitute part of the NMP. The titanium, copper and zinc compounds, e.g., oxides, can be present from alloying elements in the aluminum scrap. It is desirable to recover all useful constituents from the salt cake. Thus, the salt cake is treated to recover the salts, the insoluble constituents or non-metallic product and any remaining aluminum metal.
The salt cake can be advantageously treated in accordance with the procedures set forth in U.S. Pat. Nos. 5,102,453 and 5,227,143. However, even after such treatment, there remains the insoluble constituent or non-metallic product. U.S. Pat. No. 5,102,453 discloses the problems attendant the presence of magnesium from magnesium-containing alloys and the problems resulting from the addition of magnesium chloride to the recovery system. Namely, such addition increases the overall amount of magnesium chloride contained in the unrecoverable material or non-metallic product and even when disposed of in plastic film-lined landfills, problems still result. Thus, often the process of leaching the salt cake is not optimized to avoid disposal problems with non-metallic product.
U.S. Pat. No. 5,424,260 discloses a process for using non-metallic product from aluminum dross comprising the steps of providing a body of NMP in an aqueous slurry and adjusting the slurry composition by adding alumina or silica in an amount sufficient to form a fired ceramic product on heating.
However, there is still a great need for a process that recovers valuable products from the NMP. The present invention provides such a process.